My experience in this is that I played the entire campaign twice, once for the hard difficulty cheev and once for journals on casual, and during both I always aimed to get airborn kills with grenades. Then during mop-up sessions I did the same. Finally, I played 1-5 a few times killing the Knights with grenades only to no avail, so I tried 3-3, I shit you not, the first grenade I threw nets me the achievement. I think for those aiming for this one, 3-3 is a better choice.

I think in total I would have well over 50 airborn grenade kills but who knows how this one is supposed to work

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